Adam Levine -- When Female Fans Attack ... Beware Sharp Fingernails (VIDEO)

Adam Levine was like a hostage negotiator onstage ... confronted with an overzealous fan -- except in this case, he was also the hostage!

Levine was performing with Maroon 5 in Anaheim, CA on Monday night when a woman charged at him from behind and threw her arms around him. It wasn't a devastating blow, but Adam was visibly shocked.

Still, he didn't overreact -- this was no Afroman or Riff Raff replay ... Adam took a totally different approach, but still sustained an injury. He told the crowd the woman cut his ear with her fingernails.